Calcined Mg-rich olivine enhanced oil-well cement for anti-supercritical CO2 invasion under the high-temperature and high-pressure conditions

In carbon capture, utilization, and storage (CCUS) wells, cementing cement paste based on Class G oil-well cement and compound with CO₂ corrosion-resistance materials are often used. This study aims to investigate the effect of calcined Mg-rich olivine (CMO) particles on mechanical properties and microstructure. During the sample preparation step, since ordinary Mg-rich olivine (MO) was found to provide limited improvement in the mechanical properties of cement paste, CMO was prepared through calcination to enhance the reactivity of MO. Experiments on cement paste corrosion under high-temperature and high-pressure (HTHP) conditions were then carried out using this activated CMO. The correlation between CMO and cement hydration products content was estimated by the thermodynamic model GEMS software. Furthermore, X-ray diffraction (XRD), thermogravimetry analysis (TGA), stereo microscope, vickers micro-hardness, permeability, and scanning electronic microscopy (SEM) testing methods were used to characterize the evolution of the physical properties, phase composition and pore structure of the cement paste sample under supercritical CO₂ (ScCO₂) conditions. The cement paste with 2 % CMO had a highest compressive strength, 56.38 MPa, according to the results. However, after 28 days of ScCO₂ invasion, the compressive strength of both types of mixtures declined, although it was still 30.18 % higher than that of the CMO-0 sample. The CMO-2 cement paste showed a 5.34 % decrease in permeability, whereas the CMO-0 sample's permeability increased by 160.43 %, suggesting that the CMO-containing cement paste had a denser structure. The mechanism analysis showed that the addition of CMO as an additive can promote the prismatic Mg-Calcite formation and calcite crystallization, filling and blocking the micropores in comparison to CMO-0 samples. In CCUS wells, this dense structure improves the physical resistance and durability of Class G oil-well cement paste to ScCO₂ invasion.